Method for producing crimped regenerated cellulosic fibers



Feb. 12, 1963 A. I. BATES METHOD FOR PRODUCING CRIMPED REGENERATED CELLULOSIC FIBERS Filed June 6, 1960 United fitates Patent METHGD Filit PRZBDUCl-iNG mills FED REGEN ERATED CELLULUS KC Flhliilttl Arthur E. Bates, Wilmington, Bah, assigner to American Viscose orporation, i hiiadelphia, Pa, a corporation of Delaware 1 Filed June 6, 1966, her. No. 34,158

3 Claims. ((35. 18--5t) This invention relates to a method for producing regenerated cellulosic fibers having improved crimp and other desirable fiber properties.

The crimping of fibers in general is beneficial to improve the properties of articles manufactured therefrom. For example, carpets and other fabrics manufactured from crimped fibers usually demonstrate improved texture and durability.

US. Patent No. 2,517,694 to Howard D. Merion and Wayne A. Sissons, issued August 8, 1950, discloses artificial filaments and fibers having improved crimp and a method for producing these. Specifically the patent teaches that crimped filaments can be produced from a single viscose if the filaments are not larger than denier per filament by extruding the viscose into an aqueous acid coagulating and regenerating bath which has, because of a high total salt content, a rapid dehydrating effect upon the extruded xanthate filaments and sets up thereon an at least partially regenerated skin of substantial thickness about a still substantially liquid or plastic core. By rapid coagulation a splitting or rupture longitudinally of the filaments takes place allowing part of the plastic core to flow therethrough and become at least partially regenerated to produce a filament which in cross section comprises a periphery of about half thick skin and half thin skin or none at all. This structure enables the production of a crimped fiber after stretching and relaxing of the filament since the variation in thickness of skin produces a variation in shrinkage tendency. The crimped fibers produced in this manner are typified by high dry strength moduli and low extensibilities at break.

The present invention is concerned with a method for producing an improved crirnped rayon fiber that employs the teaching or modified teaching of Merion and Sisson Patent No. 2,517,694 along with untaught critical process steps which produce unexpected results.

it is an object of this invention to provide regenerated cellulose fibers having improved crimp.

It is another object of this invention to produce regenerated cellulose fibers having improved crimp frequency and recovery.

A still further object of this invention is to provide a method for producing highly crimped regenerated cellulosic fibers having relatively low dry strength moduli, high extensibilities and an improved crimp recovery.

It is still another object of this invention to provide a method for producing highly crirnped regenented celiulose fibers in a relatively wide denier range.

in accordance with the present invention an improved fiber comprises a regenerated cellulose filament having a thickness of up to about 40 denier, said filament having a generally helical crimp produced by having a thick skin constituting only a portion of the periphery thereof, a relatively thin or negligible skin thickness on the remaining peripheral portion thereof, the thick skinned portion being positioned on the inside or" the bends of the crimp, said filament having a dry strength of less than 2 grams per denier, a wet strength of less than 1 gram per denier and a dry extensibility or elongation modulus of greater than The improved fiber as characterized herein has a crimp frequency of from about 6 to about 20 crimps Patented Feb. 12, 1953 2?. per inch and a crimp recovery in water from about 25 to 50%.

Broadly, the method for producing improved crimped rayon filament comprises extruding a filament-forming viscose solution having a common salt test of at least 4 and up to about 8 into an acid spinning bath containing over 6 and up to 10% by weight of sulfuric acid, 0.1 to 2% by weight of zinc sulfate and from at least 17 up to 23% by weight of sodium sulfate, drawing the formed filament in a substantially stretch-free condition through a second bath containing a dilute acid solution, stretching the filament to from about 25 to of its original length, relaxing all tension on the stretched filament, sluicing the relaxed filament with an aqueous medium containing up to 4% acid, and drying the resulting crimped filament.

The step of drawing the formed filament or fiber made of a plurality of the formed filaments through the dilute acid bath prior to stretching is a critical feature of this invention which enables the production of filament or fiber having an increase of up to 300% in crimp frequency for filament of over it denier as compared to crimped filament produced by stretching the filament before or during passage through the dilute acid bath.

Viscose solutions which have been found useful in accordance with the invention have from about 27 to 40% carbon disulfide, based on the alpha-cellulose content of the pulp and preferably about 28 to 32%; from about 4.5 to about 7.5% by weight based on the viscose solution, and preferably 5 to 6.5% of sodium hydroxide; from about 7 to 12% by weight based on the viscose solution and preferably 8 to 10% of cellulose. The sodium chloride salt test for a useful viscose is from about 4 to 8.

The preferred spinning bath which Will permit good spinnability of the viscose and improved crimp in filaments extruded therein contains from about 6.5 to 7.5% of sulfuric acid; from about 0.3 to 1% of zinc sulfate; and from about 19 to 21% of sodium sulfate. The ten perature at which the spinning bath is maintained is not critical and for reasons of convenience is generally from about 40 to 50 C.

The second bath through which the formed filament is drawn is a dilute aqueous sulfuric acid solution which may or may not contain a very small amount, not over about 1.0% of zinc sulfate and which may or may not contain a small amount, not over 10% of sodium sulfate. Generally the second bath contains from about 2 to about 4% by weight and preferably from 2.5 to 3% sulfuric acid. The bath is usually of the cascade type, either horizontal or vertical, and is maintained at a temperature between al5 out 50 and C. and preferably between 75 and 8 C.

The filament or fiber made of a plurality of filaments can be stretched by wrapping for several turns around a 7 first godet revolving at one speed and then wrapping the filament several turns about the second godet revolving at a faster speed so that between the two godets the filament or fiber is stretched to the desired degree beyond its original length. The filament, in accordance with this invention is stretched after leaving the second bath to from about 25 to about 75% and preferably from about 35 to 50% of its original length. As previously stated, the filament is kept at a substantially stretch-free condition during its passage through the spinning bath and the second regenerating bath. During its passage through these baths the filament may contact some stationary guides which cause a minor amount of tension; however, the minor amount of stretching from such contact is considered negligible and is permissible for this process. Stretching of the filament is preferably carried out in air rather than in a water or other liquid bath.

The filament or fiber proceeding from the stretch step has all the tension removed therefrom. This is usually 3 performed by a cutting operation at regular intervals. The cuttings are then sluiced or washed with a hot aqueous media such as water or a dilute acid solution to promote crimping. After the sluicing operation, the cut fibers are dried.

FIGURE 1 of the drawing is a diagrammatic representation of the process of this invention.

Viscose is extruded from spinneret 2 into spinning bath 4 and formed into fiber 6 as it leaves the spinning bath. Fiber 6 passes over an idling guide 8 into a cascade type bath 10 containing dilute acid solution. The fiber then passes under idler 12 and is drawn by positively driven godet 14 which is rotated at substantially the same speed as the extrusion rate of the viscose from spinneret 2 so that the fiber 6- is in a substantially stretch-free condition during its travel through the spinning bath and cascade bath 10.

Several turns are made about the godet 14 and hook or idler guide 16. The filament then makes several turns around large godet 18 which is rotating at a faster peripheral speed than godet 14 to produce sufiicient tension on the. fiber to obtain a stretch of from. about 25' to 75% of its original. length.

The fiber 6 is then passed through cutter 26 where it is cut into small equalv lengths. These fiber lengths 22 fall into sluice box 24 wherein they are sluiced with hot water coming from several nozzles 26. Fibers 22 fall from the bottom of the sluice box 24 to a processing stage broadly designated as 28 through which they travel on belt 3%). In the processing stage 28 the fiber is washed free of acid, then desulfurized with a dilute sodium sulfide solution followed by washing, bleaching, bleach acid treatment, another Washing and treatment with a softening agent. After passing through squeeze rolls to remove excess liquid, the fiber is conducted through the dryer section 32 from which it passes to the baler or storage area.

The following examples are set forth to. demonstrate the invention.

EXAMPLE 1 A viscose consisting of 32% carbon disulfide, 6.0% sodium hydroxide and 9.0% cellulose and having a common salt test of 6.0 was used to spin denier filaments into fibers in three different procedures which varied in the location of a cascade regenerating bath subsequent to the spinning bath. In each procedure the spinning bath consisted of 6.5% sulfuric acid, 1.0% zinc sulfate and 21% sodium sulfate. The spinning speed in each procedure was 62.5 m./m-. with immersion of the formed filament for 30 inches in the spinning bath. The cascade bath contained 2.5% sulfuric acid and was maintained at a temperature at 80 C.

In procedure A the 15 denier filaments were formed by extrusion in the spinning bath to form a fiber which was stretched in air to 67.5% of its original length between godets turning at different speeds, and then drawn through the cascade bath for a distance of 12 inches with no further stretching. The fiber was then cut into short lengths, the cuttings washed in a water sluice maintained at 75 C. and then dried.

In procedure B the 15 denier filaments were formed by extrusion in the spinning bath to form a fiber which was drawn from the spinning bath on a godet with only enough tension to remove the fiber as it was formed in the bath. The fiber was then drawn through the cascade bath for a distance of 12 inches while stretching to 67.5% of its original length between two godets situated on each side of the cascade and running at different speeds to apply the needed tension. The stretched fiber was then cut into short lengths, washed in a water sluice maintained at 75 C. and dried.

In procedure C, the filaments were formed by extrusion in the spinning bath to form a fiber which was drawn through the cascade bath for a distance of 12 inches and then stretched in air to 67.5% of its original length between godets turning at different speeds to apply the necessary tension. The fiber was then cut into short lengths, washed in a water sluice maintained at 75 C. and dried.

In a comparison of the fibers prepared in the three different procedures it was found that the fiber of procedure A bad random crimps of perhaps 2 to 3 per inch. The fiber of procedure B, which is the procedure normally used in plant manufacture of crimped fibers of lesser thickness, was fairly evenly crimped with from 4 to 6 crimps per inch. The fiber of procedure C, which is that of this invention, was evenly crimped with from 14 to 18 crimps per inch.

EXAMPLE 2 This example demonstrates the range for the amount of alkali metal salt in the spinning bath.

A number of fiber samples were prepared by extruding viscose as defined in Example 1 into spinning baths in which the amount of sodium sulfate was varied. A plurality of 15 denier filaments was formed by extruding the viscose through spinnerets into separate spinning baths containing 6.5% sulfuric acid, 1.0% zinc sulfate and varying amounts of sodium sulfate with bath temperatures maintained at 50 C. The filaments were formed into fibers before leaving the spin bath. The fibers were passed through 12 inches of a cascade bath consisting of 2.5 sulfuric acid at a maintained bath temperature of C. No tension was put on the fibers except that necessary to draw them through. the cascade bath at a speed of 62.5 m./m. which corresponded substantially to the extrusion rate. The fibers were then stretched in air to 55% of their original length and cut into small lengths of a few inches. The cut fibers were washed in a water sluice at 75 C. and dried. The following table demonstrates the results obtained with spinning baths containing different amounts of sodium sulfate.

Table I Strength Elongation Sample Percent Crlmps/ N 22804 in.

Dry Wet Dry Wet From the above data it can be seen that at least 17% of alkali metal salt should be present in the spinning bath to obtain the desired crimp while the most preferable amount would be about 19%. Decreasing the amount of sodium sulfate in the given range increased the dry elongation but did not affect the strength.

EXAMPLE 3 This example is given to demonstrate the amount of spinning bath acid which is preferred for this invention.

In this experiment three fiber samples from 15 denier filaments were prepared in the same manner as those in the preceding example except that instead of varying the amount of salt, the amount of acid was varied. The spinning baths contained 1.0% zinc sulfate, 21% sodium sulfate and respectively 6, 6.5 and 7% sulfuric acid. It was found that the spinnability of the filaments formed in the bath containing 6% acid was poor while the filaments spun in the baths containing 6.5 and 7% acid was satisfactory. The crimp obtained in the filaments spun in the bath containing 6% acid was also poor while the crimp in filaments formed in spin baths containing 6.5 to 7% acid was excellent. Thus it can be seen that over 6% acid should be used and preferably from 6.5 to 7%. More acid can be used up to about 10% in the process of this invention; however, the optimum condition for preparing filaments having thicknesses in the range of l to 25 denier dictates a preference for the given preferred range.

EXAMPLE 4 This example is set forth to demonstrate the effect of zinc sulfate content of the spinning bath and amount of stretch on crimp and crimp recovery of the filaments produced in accordance with the invention.

A plurality of denier filaments was produced by extruding viscose as defined in Example 1 into spinning baths consisting of 7% sulfuric acid, 21% sodium sulfate and varying amounts of zinc sulfate. The filaments were drawn through the spin bath for a distance of 30 inches. The filaments in the form of fibers were drawn through a second bath of the cascade type in a substantially stretchfree condition at a speed of 62.5 m./m. for a distance of 50 inches. The cascade bath contained 2.5% of sulfuric acid and had a constant temperature of 80 C. The fibers were then stretched in air to varying degrees, cut into small lengths, washed and dried.

The data in the following table shows the results of this experiment.

Table II Crimp Dry Sample ZnSOt Stretch Crimps/ Recov- Dry Elongain. ery, Strength tion percent The above data demonstrates that increasing stretch increases strength and decreases elongation while the amount of crimp and crimp recovery are improved. In addition, by using an optimum amount (0.5%) of zinc sulfate in the spinning bath, improveemnt in crimp rate, crimp recovery, lower strength and higher elongation is observed. Thus, when producing fibers for carpet manufacture a reduction in the amount of zinc sulfate to about 0.5 in the spin bath permits a lower stretch to obtain fiber having the same or higher amount of crimps and a lower dry strength modulus than previously produced fibers. In addition, the reduction in zinc sulfate in the bath permits a manufacturing cost reduction.

Crimped fiber of 15 denier per filament size was also produced with the conventional procedure of stretching the fiber in the second bath. The fiber was spun with a viscose of substantially the same formulation, in a spinning bath of the same formulation, and at the same speed as samples G, H and l. A stretch of 67.5 was applied to the fiber. This fiber had 6 crimps per inch, :1 crimp recovery of 15%, a dry strength modulus of 2.56 and an elongation of 18%. Obviously, the crimped fibers of the invention are unexpectedly superior to those conventionally produced.

Example 5 This example is given to demonstrate the effect of viscose age on crimp and crimp recovery of filaments prepared in accordance with the invention.

A viscose consisting of 32% carbon disulfide, 6.0% sodium hydroxide and 9.0% cellulose was extruded into a spinning bath at different stages of ripeness. The spinning bath consisted of 7% sulfuric acid, 0.5% zinc sulfate and 21% sodium sulfate and was maintained at a temperature of 50 C. The viscose was extruded to form a plurality of 15 denier filaments which were formed into a fiber and drawn through a cascade regenerating bath for 50 inches in a stretch-free condition at a speed of 62.5 m./m. The cascade bath consisted of a 2.5% aqueous sulfuric acid solution at a temperature of 80 C. With each of the fibers formed from viscose of different ripeness, a varying amount of stretch was applied after leaving the cascade bath. In each case, after stretching the fibers were cut into small lengths, washed and dried.

The following table demonstrates the eifect of viscose age and stretch with respect to crimp. Crimp recovery is determined by first removing the crimp from short lengths of crimped fibers by a pressing and smoothing action of; the fingers. When the fibers are smooth they are dropped into shallow water in a glass beaker at room temperature. The smooth filaments crimp on immersion and they are measured by placing the beaker over a ruler. The crimp recovery is recorded by the percent contraction of the length of fiber.

Table III Sample Salt, Stretch Crimping Crimp] Crimp Test: Rate Inch Recovery 3. 7 40 Slow 3 Very little. 3. 7 30 Slow 4 15%. 3.7 60 Slow 4 4. 9 40 Fast 6 33%. 4. 9 50 Fast 8 40%. 4. 9 60 Fast 8 40%. 5. 7 40 Foster: 8 33%. 5. 7 50 Faster. 12 53%. 5. 7 60 Faster 18 50%.

From the above data it is apparent that reduction in stretch and increase in viscose age both result in decrease of speed of crimping and crimp frequency. It was also observed that the older viscose produced fiber which had a much softer hand than the younger viscose. For carpet fiber which requires firm hand for good texture, a young viscose would be preferred. Further, it was observed that fiber prepared from a viscose having a salt test of 5.7 and stretched 67.5% prior to being passed through the cascade had only 6 crimps per inch.

In the process of this invention all tension is removed from the filaments or fibers after stretching to permit sluicing and drying in a relaxed condition. This relaxation is preferably obtained by cutting the filaments or fibers into short free lengths before sluicing to obtain the crimp.

Sluicing of the relaxed fibers is carried out in an aqueous medium such as plain water or a dilute acid solution of up to about 3 or 4%. Generally the temperature of the sluicing medium is between 50 and 100 C. and prefer-ably between 75 and 85 C. The temperature and acidity of the sluice do not appear to be particularly critical but the whiteness of the fiber improves with increased acid while elongation is lowered slightly.

The speed at which the viscose is extruded and drawn through the spinning and regenerating second bath is not critical as long as the filament or fiber is not given any substantial stretching. The speed is determined somewhat by the distance over which the filament is immersed in both the spinning bath and the second bath and conversely. Generally, the spinning speed before stretching is within the range of about 40 to m./m. The distance over which the filament is immersed in the spinning bath for coagulation and at least partial regeneration is generally about 15 to 50 inches while immersion in the second bath for further regeneration is from about 10 to 75 inches and preferably from about 40 to 60 inches in order to obtain better crimping with less zinc sulfate in the spinning bath.

Fibers having filaments of 1.5, 3.0, 5.5 and 25 denier as well as those of intermediate size have been spun in accordance with the process of this invention. Fibers of all sizes up to at least 40 denier will demonstrate improved crimp and other fiber properties with this process.

Various changes and modifications may be made in practicing the invention without departing from the spirit and scope thereof and, therefore, the invention is not to be limited except as defined in the appended claims.

I claim:

1. A method for producing improved crimped rayon filament comprising extruding a filament forming viscose solution comprising from 7 to 12% cellulose based on the weight of the viscose, from 27 to 40% carbon disulfide based on the weight of the cellulose and from 4.5 to 7.5% sodium hydroxide based on the weight of the viscose, said viscose having a common salt test between 4 and 8, extruding said viscose into a spinning bath containing from over 6 and up to 10% by weight of sulfuric acid, from about 0.1 to 2% by weight of zinc sulfate and from about 17 to about 23% by weight of sodium sulfate, drawing the formed filament in a substantially stretchfree condition through a second bath containing from about 2 to 4% sulfuric acid and having a temperature of from about 50 to 100 C., stretching the filament to from about 25 to 75% of its original length, cutting the stretched filament into small lengths, sluicing the cut filament in an aqueous medium containing up to 4% acid, and drying the resulting crimped filament.

2. A method for producing improved crimped rayon filament comprising extruding a filament forming solution consisting essentially of 8 to 10% cellulose based on the weight of the viscose, from 28 to 32% carbon disulfide based on the weight of the cellulose and from to 6.5% sodium hydroxide based on the weight of the viscose, said viscose having a salt test between 4 and 8, extruding said viscose into a spinning bath consisting essentially of from 6.5 to 7.5% by weight of sulfuric acid, from 0.3 to 1% by weight zinc sulfate, and from 19 to 21% by Weight of sodium sulfate, drawing the formed filament in a substantially stretch-free condition through a second bath containing essentially from 2.5 to 3% by weight of sulfuric acid and having a temperature of from about 75 to 85 C., stretching the filament in air to from about 35 to 50%- of its original length, cutting the stretched filament into small lengths, sluicing. the cut filament with an aqueous medium containing up to 4% sulfuric acid and having a temperature from 75 to 85 C., and drying the resulting. crimped filament.

3. The method of claim 2 wherein the filament travels at a speed of from to 80 meters per minute before stretching and passes through from 15 to inches of spinning bathand from 10 to inches of said second bath.

References Cited in the-file of this patent UNITED STATES PATENTS 2,340,377 Graumann et a1. Feb. 1, 1944 2,517,694 Merion et -al. ..a Aug. 8, 1950 2,966,391 Bandel Dec. 27, 1-960 

1. A METHOD FOR PRODUCING IMPROVED CRIMPED RAYON FILAMENT COMPRISING EXTRUDING A FILAMENT FORMING VISCOSE SOLUTION COMPRISING FROM 7 TO 12% CELLULOSE BASED ON THE WEIGHT OF THE VISCOSE, FROM 27 TO 40% CARBON DISULFIDE BASED ON THE WEIGHT OF THE CELLULOSE AND FROM 4.5 TO 7.5% SODIUM HYDROXIDE BASED ON THE WEIGHT OF THE VISCOSE, SAID VISCOSE HAVING A COMMON SALT TEST BETWEEN 4 AND 8, EXTRUDING SAID VISCOSE INTO A SPINNING BATH CONTAINING FROM OVER 6 AND UP TO 10% BY WEIGHT OF SULFURIC ACID, FROM ABOUT 0.1 TO 2% BY WEIGHT OF ZINC SULFATE AND FROM ABOUT 17 TO ABOUT 23% BY WEIGHT OF SODIUM SULFATE, DRAWING THE FORMED FILAMENT IN A SUBSTANTIALLY STRETCHFREE CONDITION THROUGH A SECOND BATH CONTAINING FROM ABOUT 2 TO 4% SULFURIC ACID AND HAVING A TEMPERATURE OF FROM ABOUT 50 TO 100* C., STRETCHING THE FILAMENT TO FROM ABOUT 25 YO 75% OF ITS ORIGINAL LENGTH, CUTTING THE STRETCHED FILAMENT INTO SMALL LENGTHS, SLUICING THE CUT FILAMENT IN AN AQUEOUS MEDIUM CONTAINING UP TO 4% ACID, AND DRYING THE RESULTING CRIMPED FILAMENT. 